Another "why" comment that is valuable. Without the comment, a naive developer might very declare the values at the call site, breaking the SWT library.

gistfile1.java

public static final int BUTTON_MASK;
public static final int MODIFIER_MASK;

static {
  /*
	* These values represent bit masks that may need to
	* expand in the future.  Therefore they are not initialized
	* in the declaration to stop the compiler from inlining.
	*/
	BUTTON_MASK = BUTTON1 | BUTTON2 | BUTTON3 | BUTTON4 | BUTTON5;
	MODIFIER_MASK = ALT | SHIFT | CTRL | COMMAND;
}